The present invention relates to waterborne basecoat compositions having particular utility in multi-layer coatings such as vehicle basecoat/clearcoat (BC/CC) applications. The basecoat compositions of this invention can be used in either original equipment manufacturer (OEM) production lines or in automotive vehicle refinish (VR) body shops and the like.
Multi-layer coatings for use over the surface of automobiles, trucks and the like have been in use for years. Originally, such coating systems used organic solvents. As environmental concerns and regulations became more prevalent, such organic solvent-based systems fell out of favor. In recent years, the development of waterbome systems has increased. In particular, the development of waterborne basecoats as part of a volatile organic content (VOC) compliant basecoat/clearcoat system has increased. Many of the world""s large coatings companies have disclosed waterborne basecoats for use in basecoat/clearcoat vehicle coatings. By way of example, BASF, DuPont, ICI and PPG all have patents in this area: U.S. Pat. No. 5,204,401 (Anderson et al., BASF) teaches metallic and nonmetallic waterborne basecoats having a water-reducible acrylic resin with nonionic and acid functionality derived from vinyl monomers having nonionic and urethane functionality. U.S. Pat. No. 5,169,719 (Balatan BASF) teaches water-dilutable polyurethane/acrylic copolymers useful as the principal resin and as pigment grind resins in waterborne automotive basecoats. U.S. Pat. No. 5,157,069 (Campbell, BASF) teaches an aqueous coating comprising a nonionic dispersion of a polymer selected from the group consisting of acrylic resin, polyurethane resin (and mixtures thereof) with a nonionic water soluble rheology control polymer (such as a polyether, cellulose, cellulose derivative, polyvinylalcohol, etc.) and pigments. U.S. Pat. No. 5,066,732 (Savino et al., BASF) teaches water dispersible nonionic polyurethane resins having polyether backbones. U.S. Pat. No. 5,017,673 (Balatan, BASF) teaches water dispersible nonionic polyurethane resins having polyester backbones. U.S. Pat. No. 4,978,708 (Fowler et al., BASF) teaches an aqueous basecoat containing an anionic polyurethane resin and an anionic acrylic pigment grind resin. U.S. Pat. Nos. 4,558,090 and 4,489,135 (Drexler et al., BASF) teach a process and composition useful as a basecoat in a multilayer coating wherein the basecoat is an aqueous polyurethane. U.S. Pat. No. 5,204,404 (Werner Jr., et al., DuPont) teaches waterbased coating compositions containing an acrylic silane polymer and a polyurethane polymer. U.S. Pat. No. 5,051,464 (Johnson et al., DuPont) teaches a waterbased coating composition containing an acrylourethane pigment dispersing polymer and a binder. U.S. Pat. Nos. 5,006,413 and 4,954,559 (Den Hartog et al., DuPont) teach waterbased coating compositions containing a methylol (meth)acrylamide acrylic polymer binder and a polyurethane. U.S. Pat. No. 5,100,735 (Chang, DuPont) teaches an improved process for forming a multilayer finish on an automobile comprising using a waterborne acrylic basecoat and a high solids, solvent-based acrylic, polyester, or polyesterurethane clearcoat with an alkylated melamine formaldehyde crosslinking agent. U.S. Pat. No. 4,403,003 (Backhouse, ICI) teaches a process for producing a multilayer coating wherein an aqueous dispersion pigmented basecoat containing crosslinked microparticles is first applied. U.S. Pat. No. 4,822,685 (Perez et al., PPG) teaches a method of forming a multilayer coating over a substrate wherein an aqueous-based polyurethane dispersion is used as a pigmented basecoat. U.S. Pat. No. 4,719,132 (Porter Jr., BASF) teaches an aqueous basecoat comprising an aqueous polyurethane resin.
The present invention relates to a waterborne basecoat composition which, together with an appropriate clearcoat composition, is particularly useful as a multilayer coating system for use in both OEM and VR applications. The basecoat composition is low in VOC and can be pigmented with a broad range of pigments readily available and used in the automotive industry, including nonmetallic pigments, metallic pigments and other opalescent pigments. It is specifically designed to have good solvent and water resistance. This prevents basecoat attack and degradation by the clearcoat or topcoat and promotes clearcoat gloss and metal stability and orientation for metallic pigments. Yet, the basecoat also remains easy to clean from spraying equipment.
The waterborne basecoat composition of the present invention comprises:
a. water,
b. a polyurethane resin dispersible in water,
c. one or more resins selected from the group consisting of water-reducible resins and aqueous emulsion polymers, produced by a free-radical addition polymerization reaction, and
d. pigment.
In a preferred embodiment, the waterborne basecoat composition of the present invention is obtained by mixing two main components prior to application to the substrate:
a. one or more pigmented toner resin components, and
b. a mixing clear resin component.
In such an embodiment, each pigmented toner resin component comprises water, a resin or polymer and pigmentation for the basecoat. It should be appreciated that many of today""s popular basecoat colors are the result of a combination of two or more pigmented toner resins. Each toner resin comprises one or more resins or polymers selected from the group consisting of i) polyurethane resins dispersible in water, ii) water-reducible resins and aqueous emulsion polymers, produced by a free-radical addition polymerization reaction, and mixtures thereof. Pigments in the toner resin component comprise standard pigments such as titanium dioxide, carbon black, red oxide and the like, opalescent pigments such as micas, and metallic pigments such as aluminums. Generally, such pigments are available in the form of pigment dispersions; however, powdered pigments are also available and useful. The combination of one or more such toner resins provides the OEM painter or the VR refinisher with the desired basecoat color. A method for properly selecting the types of resins to be used in the toner components is taught herein.
In the above-mentioned preferred embodiment, the mixing clear resin component comprises:
a. one or more aqueous emulsion polymers produced by a free-radical addition polymerization reaction (particularly useful in the case of ambient cure, or forced air dry cure systems such as those used in vehicle refinish shops), or
b. a polyurethane dispersion resin in combination with a small amount of aqueous emulsion polymer (particularly useful in the case of temperature cured or bake dry systems such as those used in OEM production lines).
Preferred basecoat ingredients are more fully described below. In addition, the criteria for determining the requisite combinations of pigment and resin in each preferred component are described in more detail.
Accordingly, it is an object of this invention to teach a novel waterborne basecoat composition particularly useful in multi-layer basecoat/clearcoat applications.
It is a further object of this invention to teach a multi-layer coated substrate wherein the basecoat layer comprises the novel waterborne basecoat described herein.
It is yet a further object of this invention to teach a process for coating a substrate with a multi-layer coating composition comprising the novel waterborne basecoat described herein.
These and other objects will become more apparent from the detailed description of the invention below.
As described briefly above, the present invention relates to a waterborne basecoat composition which, together with an appropriate clearcoat composition, is particularly useful as a multilayer coating system for use in both OEM and VR applications. The basecoat composition is low in VOC and can be pigmented with a broad range of pigments readily available and used in the automotive industry, including nonmetallic pigments, metallic pigments and other opalescent pigments.
The waterbome basecoat composition of the present invention comprises:
a. water,
b. a polyurethane resin dispersible in water,
c. one or more resins selected from the group consisting of water-reducible resins and aqueous emulsion polymers, produced by a free-radical addition polymerization reaction, and
d. pigment.
In a preferred embodiment, the waterborne basecoat composition of the present invention is obtained by mixing two main components prior to application to the substrate:
a. one or more pigmented toner resin components, and
b. a mixing clear resin component.
It should be appreciated that many of today""s popular basecoat colors are the result of a combination or mixture of two or more pigmented toner resins. Each such pigmented toner resin component comprises water, a resin or polymer and pigmentation for the basecoat. In the present invention, each toner resin comprises one or more resins selected from the group consisting of i) polyurethane resins dispersible in water, ii) water-reducible resins and aqueous emulsion polymers, produced by a free-radical addition polymerization reaction, and mixtures thereof. Pigments in the toner resin component comprise standard pigments such as titanium dioxide, carbon black, red oxide and the like, opalescent pigments such as micas, and metallic pigments such as aluminums. The mixture of one or more such toner resins, together with the mixing clear component, provides the OEM painter or the VR refinisher with the desired basecoat color. A method for properly selecting the types of resins to be used in the toner components is taught herein.
In the above-mentioned preferred embodiment, the mixing clear resin component comprises:
a. one or more aqueous emulsion polymer resins produced by a free-radical addition polymerization reaction (particularly useful in the case of ambient cure, or forced air dry cure systems such as those used in vehicle refinish shops), or
b. a polyurethane dispersion resin in combination with a small amount of aqueous emulsion polymer (particularly useful in the case of temperature cured systems such as those used in OEM production lines).